A straight pipe after the cat will just be noisy, without that much performance, you need some back pressure for proper valve closure. A straight pipe in place of the cat (meaning a straight pipe only), will burn your valves during hi rpm running and when you shut it down, cold air will rush in and crack your valves.

 

Not exactly true Diesels with a gross vehicle rating of 8500lbs or less are not subject to emission inspections, over 8500lbs they are subject to roadside inspection and in the NYMA they are required to get an annual inspection.